1. Field of the Invention
The present invention relates to a toner for use in electrophotographic image forming apparatuses such as a copier, an electrostatic printing, a printer, a facsimile machine, and an electrostatic recording. The present invention also relates to a developer, a toner cartridge, an image forming apparatus, a process cartridge, and image forming method using the toner.
2. Discussion of the Background
In electrophotographic image forming apparatus and electrostatic recording apparatus, an electric or magnetic latent image is developed into a toner image that is visible. For example, in electrophotography, an electrostatic latent image is formed on a photoreceptor and developed into a toner image with a toner. The toner image is transferred onto a recording medium such as paper and fixed thereon by heat, etc.
Generally, a toner comprises colored particles comprising a binder resin, a colorant, a charge controlling agent, etc. A toner is manufactured by various methods such as pulverization methods, suspension polymerization methods, dissolution suspension methods, emulsion aggregation methods, phase-transfer emulsification methods, and elongation polymerization methods.
Specific resins generally used for toner include thermoplastic resins such as styrene-acrylic resins, polyester resins, and polyol resins. In particular, polyester resins are widely used because of having a relatively large molecular weight and a high glass transition temperature while having a low softening point. Polyester resins also have high strength. Therefore, polyester resins are preferably used for toners which are required to be fixed at low temperatures (this property is hereinafter referred to as “low-temperature fixability”), such as toners for producing full-color images (hereinafter “full-color toners”).
The coloring power and color reproducibility of a full-color toner depend on the dispersion state of a colorant in a binder resin. In a case in which the colorant is unevenly dispersed in the binder resin to make the toner opaque, the toner may not reliably reproduce the secondary colors. Therefore, it is preferable that the colorant is evenly dispersed in the binder resin to make the toner transparent.
Most organic pigments, such as azo pigments usable for yellow and magenta toners, generally have a hydrophilic chemical structure. Carbon blacks usable for black toners generally have an acid or basic polar group. Such pigments and carbon blacks are not always sufficiently dispersed in resins, depending on the properties thereof. It is generally known that to provide a polar group in a resin is effective for improving dispersibility of colorants therein. However, there is concern that the polar group may affect thermal and electric properties of the resultant toner.
Japanese Patent No. 2909873 discloses a toner including a lactic acid-based resin, one terminal group being hydroxyl group and the other terminal group being an alkyl ester of a carboxylic acid or a salt of a carboxylic acid. For example, a toner including a polylactic resin which is formed from L-lactide is disclosed therein. The toner may express low thermoplasticity when fixed because such a resin is crystalline and has a high melting point. As a result, the resultant image may have low transparency and low color saturation.
Japanese Patent Application Publication No. 09-274335 discloses a toner including a polyester resin obtained from dehydration polycondensation of a lactic acid and a tri- or higher functional oxycarboxylic acid. The tri- or higher functional polar group makes the resultant resin have a cross-linking structure. Therefore, the resultant resin may not melt quickly, resulting in poor transparency and color saturation.
Both Japanese Patent Nos. 3785011 and 3779221 disclose a toner including a polylactic-based biodegradable resin and a terpene phenol copolymer. Such a toner may not have sufficient low-temperature fixability and hot offset resistance at the same time.